Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $82.96   11.719%   $92.6821   $92.68   $92.70   $92.70  
  Purchase #2 $178.91   10.274%   $197.2912   $197.29   $197.30   $197.30  
  Purchase #3 $85.93   4.243%   $89.576   $89.58   $89.60   $89.60  
  Purchase #4 $103.78   11.831%   $116.0582   $116.06   $116.05   $116.10  
  Purchase #5 $239.86   6.229%   $254.8009   $254.80   $254.80   $254.80  
  Purchase #6 $188.42   3.774%   $195.531   $195.53   $195.55   $195.50  
  Purchase #7 $178.39   8.134%   $192.9002   $192.90   $192.90   $192.90  
  7 purchase totals = $1,058.25       $1,138.8396   $1,138.84   $1,138.90   $1,138.90